This invention relates to a heating assembly for a heat treating furnace. More particularly, the invention relates to a heating assembly of the type in which an electrical resistance heating element such as a graphite rod is disposed within a radiant tube. To prevent detrimental oxidation of the heating element at high temperatures, the tube often is purged of oxygen and is filled with a protective gas such as nitrogen.
Heating elements which are protected by a non-reactive gas are disclosed in Weinheimer et al. U.S. Pat. No. 2,147,071; Kerschbaum U.S. Pat. No. 2,215,587 and Peyches U.S. Pat No. 2,253,981. With prior arrangements, however, difficulty has been encountered in maintaining the gas at a proper pressure. The pressure of the gas changes in response to temperature fluctuations and, in addition, there may be some leakage of gas from the tube. If the pressure falls below a safe value, oxygen or other reactive gases may enter the tube and damage the heating element. On the other hand, an excessively high pressure may rupture the tube or the seals thereof.